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Hey guys,

I recently acquired an 85 F250 with the 7.5l 460 gas engine, and the brakes have been a little squishy. After checking and cleaning all the brakes, I went to bleed the brake lines and discovered a small brake fluid leak from a part that I can’t identify. I couldn’t find a comprehensive diagram of the brake lines online, but the part in question is connected to the rear axle vent tube. I had trouble bleeding the rear brakes (even after inspecting and cleaning the bleeder valves - which looked great), but the front brakes bled beautifully. I was wondering if this leaking component could be the cause before I investigate the possibility of a blockage or leak elsewhere. If this is the source of the problem, I would like to know what it’s called so I can fix or replace it.

Thanks in advance for your response!

52645

52646
 

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It's difficult to tell from the photos, but that looks like the load proportioning valve. Does it move with the suspension?
Thank you! That's absolutely what it is. The brake supply line goes into there before it enters the axle vent tube and splits the brake lines into each side of the rear brakes. I might get lucky finding one at the salvage yard, but it seems like I'm SOL on trying to find a new one. What are my options at this point now that I can be fairly confident that's the issue? Is there a way to safely delete/bypass it?
Thanks again
 

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You can bypass the valve, but braking distances would increase dramatically because equal pressure would then go to the front and rear, causing the rear brakes to lock up early if the truck is unloaded (the front brakes do most of the braking when empty). This is especially dangerous in the rain. If you absolutely cannot find a stock proportioning valve, off- road and circle track race suppliers (maybe check several race catalogs) sell them, but they are all dash mounted so the driver can adjust them mid race. I will ask some racer buddies if one is made with remote adjusting, but then you are getting into custom fabrication which is big bucks if you don't have the shop, tools, and experience. I will research this a little for you, but in the meantime, ask a brake shop what they do for parts.
 

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I just talked with a friend who had the same problem with his '86. As you discovered, new or rebuilt valves are non-existent. He bypassed the valve at the rear axle and installed a manually adjustable proportioning valve like I mentioned in the previous post, but mounted it under hood near the master cylinder. A little experimentation with the adjustment (do it on a dirt road) and you will get the settings right for load and no load conditions. That's a lot of work for a part that should be available, but so be it. He no longer owns the truck or else I would get photos for you. Sorry.
 

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I just talked with a friend who had the same problem with his '86. As you discovered, new or rebuilt valves are non-existent. He bypassed the valve at the rear axle and installed a manually adjustable proportioning valve like I mentioned in the previous post, but mounted it under hood near the master cylinder. A little experimentation with the adjustment (do it on a dirt road) and you will get the settings right for load and no load conditions. That's a lot of work for a part that should be available, but so be it. He no longer owns the truck or else I would get photos for you. Sorry.
Wow, thank you so much. You really went above and beyond! I'll be sure to look into an adjustable proportioning valve and call around to some brake shops to see about part options.
 

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Wow, thank you so much. You really went above and beyond! I'll be sure to look into an adjustable proportioning valve and call around to some brake shops to see about part options.
Good luck to you. I like old trucks. They seem to develop their own character that cars somehow lack.
 

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Good luck to you. I like old trucks. They seem to develop their own character that cars somehow lack.
I've always been fond of old trucks for the very same reason. Makes it a little too easy to get emotionally attached to them though...or maybe that's just me ;). In any case, I still haven't been able to fully address it yet, since I had back-to-back carburetor and electrical issues that demanded my attention. I also haven't been able to locate an adjustable valve that will work to save my life, so it looks like I might need to bypass the old proportioning valve. Before I do so, I want to ensure I get all the components and know the proper sequence of steps to avoid a huge mess of brake fluid - along with the obvious safety considerations. It looks like the rigid metal brake line has a threaded male end connection that screws onto the proportioning valve, and then a flexible rubber brake line goes from the proportioning valve to the rear axle. I'm assuming that finding a flexible line with female threads that will connect to the existing metal brake line will be easy enough, but I'm not sure what type of connection is used to connect the rubber line to the rear axle. Unless I'm overthinking it, I can't imagine that a typical hose clamp can be used due to the high pressures it will be subjected to. Any recommendation on how I should proceed?
Thanks in advance! I really appreciate it.

Here's some more photos - hopefully, to provide some clarity on what I'm dealing with:
52812
52813
52814
52815
 

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Is it possible to bypass the valve by connecting the lines with a brass brake line coupler? As to that fitting that goes to the axle, and this is from memory, I think that piece is just a "T" fitting, but I don't recall if the hose is threaded into the fitting or pressed. You might have to reengineer the entire brake line system from the valve connection to the rear axle brake lines. Fortunately, aftermarket brake lines and fittings are commonly available and not too expensive. Please let me know what you find and I will have another look at my Bud's '86 when he returns from out-of-state.
 

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Is it possible to bypass the valve by connecting the lines with a brass brake line coupler? As to that fitting that goes to the axle, and this is from memory, I think that piece is just a "T" fitting, but I don't recall if the hose is threaded into the fitting or pressed. You might have to reengineer the entire brake line system from the valve connection to the rear axle brake lines. Fortunately, aftermarket brake lines and fittings are commonly available and not too expensive. Please let me know what you find and I will have another look at my Bud's '86 when he returns from out-of-state.
Thanks Baja. The brake line coupler is an interesting thought, and I think you're correct about the axle fitting being a simple "T". It looks like the line is pressed onto the axle "T" fitting. With that being the case, I am only familiar with rubber lines with threaded ends, and have no idea how to properly press the line onto the fitting. I was hoping that I could find a compression fitting (or some other form of coupling) that's commonly used for metal brake lines but I haven't had any luck. Cutting the rubber line near the axle with the pressed end still connected, and adding a compression fitting/coupling to attach a new brake line with the other end threaded for connecting to the metal line would have been too easy.
 

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I would not try to press a metal line into the fitting because I don't know how to, either. I would, instead, eliminate the fitting entirely and use a threaded brass "T" brake fitting connected to where the metal brake line feeds into the rear. I would try to attach the fitting rigidly to the axle, but the only way I can think of is a metal strap. From there use rubber lines. I would use new ones since they are not too expensive and you've already done the work removing the old ones. Rubber hoses are available in various lengths. If you do get into any custom metal line fabrication, remember that it is very important to double flare the ends. When done it's time to bleed the system. Bleeding can be done very easily or it can be difficult to do with poor results, such as a spongy pedal. I use a power brake bleeder (see photo) It is one of those tools you wonder how you got by without. PS. Please ignore how dirty the project car is in the photo. Best of luck! IMG_3691 (1).jpg
 

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If you have a hydraulic shop in the area, they may be able to hook you up with something.We have one near my work that has made all sorts of crazy things for us.
 
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